The present invention relates to a catalyst system and a process for the preparation of homopolymers and copolymers of alpha monoolefins at from 20.degree. to 160.degree. C., especially from 50.degree. to 120.degree. C., and under a pressure of from 1 to 100, especially from 20 to 70, bar, by means of a catalyst system comprising
(1) a titanium halide of the formula EQU TiCl.sub.3.mAlCl.sub.3 PA1 where m is a number from 0 to 0.5, especially from 0.1 to 0.4, PA1 (2) an optional coordination complexing agent, and PA1 (3) an aluminum-alkyl of the formula ##STR1## where X and Y are each alkyl of not more than 8, especially not more than 2, carbon atoms, and Z is chlorine or alkyl of not more than 8, especially not more than 2, carbon atoms, with the proviso that (I) the molar ratio of titanium halide (1):complexing agent (2), if present, is from 1:1 to 20:1, especially from 3:1 to 6:1, (II) the molar ratio of titanium halide (1):aluminum-alkyl (3) is from 1:1 to 1:20, especially from 1:2 to 1:15 and (III) the titanium halide (1) and the complexing agent (2), if it is used, have been milled together before use to form a coordination complex. PA1 (1) titanium halide of the formula EQU TiCl.sub.3.mAlCl.sub.3 PA1 where m is a number from 0 to 0.5, especially from 0.1 to 0.4, PA1 (2) an optional coordination complexing agent which can be, among many other compounds, a benzoic acid ester of the formula ##STR2## where R.sup.1 is alkyl, preferably C.sub.1 -C.sub.8, or aromatic, preferably n-butyl, and PA1 (3) an aluminum-alkyl of the formula ##STR3## where X and Y are each alkyl of not more than 8, especially not more than 2, carbon atoms, and Z is chlorine or alkyl of not more than 8, especially not more than 2, carbon atoms, with the proviso that (I) the molar ratio of titanium halide (1):complexing agent (2), if used, is from 1:1 to 20:1, especially from 3:1 to 6:1, (II) the molar ratio of titanium halide (1):aluminum-alkyl (3) is from 1:1 to 1:20, especially from 1:2 to 1:15 and (III) the titanium halide (1) and the complexing agent (2), if it is used, have been milled together before use to form a coordination complex, wherein the catalyst system is employed which contains, as a further component (4), a sterically unhindered phenolic compound of the formula ##STR4## where n is an integer from 1 to 4, one of R.sup.1 and R.sup.2 is hydroxyl and the other is hydrogen, and R.sup.3 is a saturated hydrocarbon radical of not more than 30, especially not more than 24, carbon atoms, which contains at least one and not more than 4 ether groups, ester groups, and/or ketone groups or thioether groups or sulfonyl groups, or a nitrogen-containing heterocyclic ring structure such as 1,3,5-triazine-2,4,6 (1H,3H,5H)-trione, or an aromatic ring structure such as 1,3,5-trimethyl-2,4,6-trimethylene. The molar ratio of aluminum-alkyl (3):unhindered phenolic compound should be from 1:1 to 40:1, especially from 3:1 to 25:1.
Processes of this type are known. Their special feature relative to comparable processes is in the specific nature of the catalyst system used, typical examples being given in U.S. Pat. Nos. 4,120,823, 4,154,699, and 4,154,700, issued Oct. 17, 1978 and May 15, 1979, respectively.
The specific modifications of the catalyst system are made in order to achieve particular objectives, for example the following:
(a) Catalyst systems which on polymerization of alpha monoolefins, especially propylene, give polymers with a relatively high proportion of stereoregular (=isotactic) polymer.
(b) Catalyst systems which can give an increased yield of polymer, namely systems of increased productivity (systems where the amount of polymer formed per unit weight of catalyst system is increased).
(c) Catalyst systems which introduce less halogen into the polymer, which is achievable by increasing the yield according to (b) and/or by employing a titanium halide which contains very little halogen.
(d) Catalyst systems which retain a constant or relatively constant activity maximum over a very long time, which is of substantial importance for the catalyst yield.
(e) Catalyst systems which make it possible, by increasing the polymerization temperature, to increase the conversion without a significant reduction in the stereoregularity of the polymers, an effect which is generally desirable, especially in dry phase polymerization.
(f) Catalyst systems by means of which--especially at relatively high polymerization temperatures--the morphological properties of the polymers can be influenced in a particular way, for example, in giving a uniform particle size and/or reducing the proportion of fines and/or giving a high bulk density. These factors may, for example, be significant in respect of technical control of the polymerization system, of working of the polymers, and/or processability of the polymers.
(g) Catalyst systems which are simple and safe to prepare and easy to handle; for example, systems which can be prepared in (inert) hydrocarbon auxiliary media.
(h) Catalyst systems which make it possible, where the polymerization is carried out in the presence of a molecular weight regulator, especially hydrogen, to manage with relatively small amounts of regulator. This can be significant; for example, in respect to the thermodynamics of the process.
(i) Catalyst systems which are tailored for specific polymerization processes; for example, catalysts which are suited either to the specific peculiarities of suspension polymerization or to the specific peculiarities of dry phase polymerization.
(j) Catalyst systems which give polymers having a pattern of properties which makes them particularly suitable for one or another field of use.
(k) Catalyst systems which provide a particularly desirable polymer morphology in finished products, such as blown films or blow-molded bottles, etc. with controlled crystallinity, uniformly nucleated spherulitic structure, and good optical clarity.
Experience to date has shown that amongst the various objectives there are some which can only be achieved by special embodiments of the catalyst system if other objectives are lowered. Under these circumstances it is, in general, desirable to find embodiments which not only achieve the particular objectives but also demand minimum lowering of other desirable objectives.
It is an object of the present invention to provide a novel embodiment of a catalyst system by means of which better results can be achieved--for similar objectives--than with conventional embodiments. I have found that this object is achieved with a catalyst system of the type defined at the outset, which contains, as a further component (4), a particular sterically unhindered phenolic compound.
It is known to use hindered phenolic compounds to achieve advantages similar to those in the present invention as disclosed in U.S. Pat. No. 4,260,710, issued Apr. 7, 1981, and based upon German Laid Open Application DAS 2,841,645. Thus, the concept of incorporating hindered phenolic anti-oxidants in a polymerization catalyst system, for the purpose of stabilizing the resin produced, is not new. It has been proposed, for example, in U.S. Pat. No. 4,170,589, in British Patent Specification No. 1,546,912, and in Netherland Patent Application No. 7,607,396. None of the above references suggest the use of unhindered phenolic compounds. In fact, the presence of a radical capable of providing steric hindrance greater than that of an ethyl group is specifically stipulated in the British Patent Specification and the Netherland Patent Application. Furthermore, it is stated in the Netherland Patent Application that when unhindered phenolic compounds are used in the catalyst in place of hindered phenolic compounds, inferior catalyst activity is the result. U.S. Pat. No. 3,150,122 discloses salicyclic acid (o-hydroxybenzoic acid) as a catalyst modifier and says that esters can be used also. This obviously is a sterically hindered compound. Furthermore, it is stated at column 6, line 15, that the phenolic compounds used therein decrease catalyst activity whereas the sterically unhindered phenolic compounds of the present invention increase catalyst activity.
I have found that the opposite is true. The unexpected and surprising features of the present invention are that the performance of the catalyst itself is improved, for example, with respect to catalyst productivity and stereospecificity, and that this improvement can be obtained in the absence of an ortho-substituent capable of providing steric hindrance.